1. Field of the Invention
The present invention relates generally to methods and apparatus useful in the assembly and packaging of semiconductor integrated circuits (ICs) or chips, and more particularly, for notching lead wires at a precise length to facilitate severing the lead wires at the location of the notch. More particularly still, the present invention relates to notching the lead wires bonded to IC chips without substantially deflecting the lead wires from an orthogonal orientation relative to the chip, thereby facilitating insertion of the lead wires into throughholes in a printed circuit board to which the IC chip is attached.
2. Description of the Prior Art
The present trends in the computer industry are toward higher capacity processing, represented in some instances by faster switching speeds For example, gallium arsenide (GaAs) has been utilized as the base IC semiconductor chip material because of its increased switching speeds. But with increased switching speeds comes the problem of capacitance in the lead wires between components. A given amount of capacitance in a wire will attenuate a higher frequency signal, such as the type generated with faster switching speeds, by an amount greater than the same capacitance will attenuate a lower frequency (slower switching speeds) signal. The total capacitance of a wire increases with the length of the wire. Therefore, in order to capitalize on the faster switching speeds available with GaAs, the capacitance in the lead wires becomes important and the length of the lead wires and the distance between components being connected by the lead wires must be minimized. As a result, the length of the conductors connecting the ICs has been reduced, to reduce the electron transit times and to reduce the capacitance in the lead wires and other conductors, thereby enhancing performance.
One technique of attaching ICs to printed circuit boards involves directly inserting the lead wires from the IC chip into the through holes in the printed circuit board, thus directly connecting the IC chip to the PC board by the lead wires. This technique eliminates the use of the plastic package in which IC chips are commonly packaged, the curved and somewhat lengthy lead wires within the plastic package, and the connection pins extending from the package into a connector. One example of this technique is disclosed in U.S. Patent Application Ser. No. 376,156, filed June 30, 1989, for LEAD BONDING OF CHIPS ONTO CIRCUIT BOARDS ND CIRCUIT BOARDS ONTO CIRCUIT BOARDS.
The attachment of these lead wires to the electronic component is an exacting process requiring close tolerances. Accordingly, when using these techniques with GaAs chips, relatively short lead wires are attached to the chip and inserted directly into aligned holes in a printed circuit board. The chips are thus positioned side by side and stacked in a closer relationship. The holes into which the lead wires are directly inserted typically have a diameter of only about 5 mils, and the lead wire has a diameter of about 3 mils. As many as fifty or so lead wires may be connected to each chip. It can be appreciated that in order for the lead wires to be reliably inserted into the holes in the circuit board, the lead wires must be uniformly straight and of a uniform length. If the lead wires are not straight for alignment with the holes in the circuit board, a technician using a microscope will have to straighten each lead wire individually in order to make them fit into the holes in the circuit board.
Current devices for cutting lead wires on GaAs components involve notching the wire A notch is first made and then an axial force is applied on the wire away from the chip to separate the wire at the notch by tensile separation force. This prior art device utilizes a pair of separate blades which extend towards the wire and simultaneously close together to cut or notch the wire. The blades also open up while simultaneously retracting from the wire. It can be appreciated that, with the wires having a diameter of only 3 mils, this device often bends or deforms the orientation of the wire by pushing and pulling on the wire in the direction of the extension and retraction of the blades, respectively. Furthermore, the degree or amount by which the two separate blades are closed together is difficult to accurately control to create a notch of a specified depth, when the inward movement of the blades is related to their forward extension.
It is to overcome these and other shortcomings in the prior art and to provide a system for cutting lead wires so that they are dependably straight and alignable with predesignated holes in a circuit board that the present invention was developed.